Ice T, NWA and Eazy E

Nice emcees back in the day, created a whole new era for rap, but not necessarily for hiphop, i feel they took the true essence away from it with 'Gangsta' rap

Public Enemy

^Dope. Fight the power was the shit, a very good choice, not the best by todays standards i agree, but these guys were pioneers.

DMX

I admit to not being a big DMX fan, i dont like the whole 'Thug' concept, sorry. .

Eminem

Very talented lyricist, not scared to bring out his real feelings and express them poetically, very good choice my man.

You Should Listen Too:

Run DMC - Pioneers along with Public Enemy, chances are if you like P.E you'll like these guys too.
Tribe Called Quest - always the positive feel to them, gave me a different take on life witht heir music.

Aesop Rock: This kid is phenominal with his imagery and concepts, he's more for the backpacker era but i think you should at least give him a listen.